Liquid crystal display (LCD) has the advantages of portability, low power consumption, low radiation, and low cost, and has been widely used in various portable electronic devices such as notebooks, tablet PCs, mobile phones, televisions, video cameras, and the like.
Wide viewing angle is the mainstream development of an LCD. Presently, portable electronic devices such as notebooks, tablet PCs, mobile phones are adopted with wide viewing angle technology, so that users can see images on the LCD without distortion when viewed from different viewing angles. However, when using a portable electronic device in public places, the wide viewing angle design of conventional LCD cannot effectively protect the privacy of the user, and the images displayed on the LCD can be easily viewed by a bystander from a squint direction. Thus, in addition to the needs for a wide viewing angle, LCDs capable of being adjusted to a narrow viewing angle are thus developed in order to protect modern people's needs of privacy in public places.
The LCD generally includes a TFT (thin film transistor) array substrate, a CF (color filter) substrate, and a liquid crystal layer disposed between the TFT array substrate and the CF substrate. Currently, LCDs having wide viewing angle includes IPS (in-plane switching) type LCDs and FFS (fringe field switching) type LCDs. For an IPS or FFS type LCD, the pixel electrode and the common electrode are formed in the TFT array substrate. In order to control the viewing angle of the LCD, a viewing angle control electrode is formed in the CF substrate for controlling the viewing angle of the LCD. By applying an AC (alternating current) voltage to the control electrode, an electric filed is generated between the array substrate and the CF substrate to cause the liquid crystal molecules in the liquid crystal layer to rotate, whereby the viewing angle of the LCD is changed.
Referring to FIG. 1, the AC voltage applied to the control electrode may be generated by an oscillating circuit 6. The oscillating circuit 6 receives a DC (direct current) voltage from a programmable power IC 5, and then generates and outputs an AC voltage based on the received DC voltage. Since the amplitude of the AC voltage is determined by the magnitude of the DC voltage, when the programmable power IC 5 generates and outputs DC voltages with different magnitudes to the oscillating circuit 6, the oscillating circuit 6 will generate AC voltages having different amplitudes based on these DC voltages. The generated AC voltages having different amplitudes can then be applied to the control electrode to modulate the viewing angle of the LCD, so that the LCD can obtain different viewing angles. In FIG. 1, it is the programmable power IC 5 acting as a power conversion circuit for providing different DC voltages. However, the power conversion circuit is packaged in a programmable power IC, its driving ability is limited, and the cost is relatively high.